Many products, including consumer and professional products, are more effectively used by an end user when the product includes a feature that can communicate or signal to the user a particular condition or a relative level or degree of use. An example of a visual, communicative feature is a wetness indicator made by applying a color-changing composition to a substrate. Wetness indicators can either indicate a change in condition or a degree of use through a change from colorless or largely colorless to colored or through a change in color intensity.
Exemplary conditions that could be monitored using a wetness indicator include physical conditions such as the presence of moisture and chemical conditions. Exemplary consumer products that could be more effective and deliver more benefits to end users by incorporating a suitable wetness indicator include absorbent articles, such as diapers, training pants, incontinence products, or feminine hygiene pads. Other exemplary consumer products include facial tissues, bath tissue, paper towels, household cleaning items and personal cleaning wipes. Exemplary professional products that could be more effective and deliver more benefits to end users by incorporating a suitable wetness indicator include products for medical use, safety garments, industrial cleaning products and nonwoven materials. Many consumer and professional products have synthetic polymeric substrates incorporated therein which often serve as liquid barriers.
Wetness indicators are well known and are available in various forms. Desirable performance attributes include stability in high relative humidity conditions and the ability to change from colorless or largely colorless to colored when it is most meaningful to indicate a change to the user, that is, upon being wetted with an aqueous liquid. It may also be desirable for the wetness indicator to have a distinct color change to aid the user in identifying the physical condition change in the product.
Standard room temperature and standard relative humidity are the conditions that are maintained in most homes and work areas. Standard room temperature and standard relative humidity is typically accepted as the temperature range of 20° C. to 25° C. at a range of 40% to 60% relative humidity (American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (ASHRAE)). Most color-changing compositions, where the color change is due to the color-changing composition being wetted with an aqueous liquid, are stable under standard temperature and relative humidity conditions. Without being bound by theory, it is believed that color-changing compositions where the color change is due to the color-changing composition being wetted with an aqueous liquid are no longer able to maintain their original color state when standard relative humidity conditions are exceeded. For example, a color-changing composition printed on a polymeric substrate of a diaper may experience premature exposure to conditions other than standard room temperature and standard relative humidity during the manufacturing process, warehouse storage, product distribution and end user storage up until the time of use. Premature exposure of the color-changing composition to levels of relative humidity higher than standard relative humidity can affect the indicator efficacy such that the end user will not receive visual communication of the change when the color-changing composition is wetted with an aqueous liquid. This happens when the wetness indicator prematurely experiences a color change prior to being wetted with an aqueous liquid.
While the color-changing compositions known in the art provide certain benefits, there remains a need for a color-changing composition that remains stable in high relative humidity conditions. There also remains a need for the color-changing composition to change to a higher intensity color when the color-changing composition becomes wetted with an aqueous liquid. There remains a need for a color-changing composition that is durable, non-leachable, water-resistant, and water-insoluble. There further remains a need for a color-changing composition that can be applied to substrates using a printing technique at room temperature. In addition to the needs identified above, there are unmet needs associated with using color-changing materials as components of personal care absorbent articles, such as disposable diapers. In particular, there is a need for a color-changing composition that maintains its efficacy when applied to an outer cover material.